>Step by step

Exploring octaves in theory and in use

1 An octave is probably the simplest interval to define – it’s the shortest distance between two notes that share the same letter name. As discussed earlier on in the intro, here’s a typical example of a C major scale, played over one octave, eight notes from C to C, which just happen to be the white notes on a piano keyboard. 2 However, as we’ve seen, there are twelve actual note pitches contained within an octave, rather than the eight you’d presume from its name. The nonscale tones – the notes that aren’t in the scale – are overlooked. So the term ‘octave’ just relates to the notes in the scale, with the eighth note the repeat of the root note, but an octave higher. 3 Here’s how an octave interval looks, both in a traditional score and in your DAW’s piano roll editor. When MIDI was first dreamt up back in the 80s, each note was assigned a number from 0-127, with middle C being 60. Luckily, this range means that MIDI can easily accommodate all 88 keys found on a normal piano keyboard, and then some. 4 Conventional MIDI notation labels octaves with numbers. On a standard 49-note MIDI controller keyboard, spanning four octaves, the lowest note will be C1 and the highest C5. To play notes beyond these extremes, most controllers will have an octave shift button that transposes the entire keyboard an octave up or down with each press. 5 Because musical notes exist as vibrations of air, a bit like ripples in water, the pitch of any note can be represented mathematically. Each note has its own frequency, and this is the speed at which it makes the air vibrate, expressed in Hertz. For example, a synth set to concert pitch playing middle C is generating a note at a frequency of 261Hz. 6 Shown here are the frequencies of all of the notes that make up an octave, and it reveals an interesting fact. The frequency of the note at the top of the scale, C4, is 522Hz – exactly twice the frequency of the note at the bottom, C3 – one octave below it. Each note’s frequency is 1.059 times the frequency of the note immediately before it.

7 So now we’re clear on what an octave actually is, what use is it in the real world? There are loads of examples of melodies in popular songs that contain octave jumps. One that springs straight to mind is Somewhere Over the Rainbow from the Wizard of Oz. “Some” is on D3, while “where” is an octave higher on D4. 8 Another example of an octave leap is the gliding, alternating synth octaves found in classic hip-hop and R&B tracks, like Ciara’s Goodies. Here’s a typical example, with a monosynth lead sound gliding between C4, C5 and C6. Looking at the synth’s display, you can see that each octave we go up, the frequency of the sound’s waveform doubles. 9 One effect that’s pretty popular in the mainstream right now is the use of a vocal doubled with a pitchshifted low octave. Here’s one way to achieve this – we’ve got a snippet of a track here with a sampled vocal. On the vocal track, I’m going to insert a send to an aux channel loaded with a pitchshifter plugin called Soundtoys Little AlterBoy. 10 Because there are twelve semitones in an octave, to get the effect of a low octave double we need to set the Pitch control to -12. We can use the Formant control to make it sound a bit more like a male backing singer, then blend it in with the original vocal using the aux return channel’s fader. 11 Finally, another useful trick with octaves is in a string arrangement: doubling a single violin part with high octaves is a great way to thicken the sound. The violin in this piece is playing in the instrument’s lower register, and is getting a bit lost in the mix as it’s occupying the same frequency range as the piano chords. 12 If we duplicate the track a couple of times, and transpose one copy up one octave and the second up two octaves, we get a stack of violins, each playing the same part in three octaves. Effectively, we still hear all this as just one note, but the thicker timbre of the extra registers all playing together makes it sound a lot clearer and more epic.